Bottom Line:
Neurodegeneration in AD has been associated with aberrant signaling through the cyclin-dependent kinase-5 (CDK5) pathway via its activators p35/p25; however, the role of CDK5 in the mechanisms of defective adult neurogenesis in AD is unknown.These conditions resulted in impaired maturation and neurite outgrowth in vitro, and these effects were reversed by pharmacological or genetic inhibition of CDK5.Moreover, potential therapeutic approaches could focus on modulating the aberrant activity of CDK5 to target the neurogenic and neurodegenerative alterations in AD.

ABSTRACTRecent studies show that in Alzheimer's disease (AD), alterations in neurogenesis contribute to the neurodegenerative process. Neurodegeneration in AD has been associated with aberrant signaling through the cyclin-dependent kinase-5 (CDK5) pathway via its activators p35/p25; however, the role of CDK5 in the mechanisms of defective adult neurogenesis in AD is unknown. First, to study AD-like abnormal activation of CDK5 signaling in an in vitro model of neurogenesis, neuronal progenitor cells (NPCs) were infected with a viral vector expressing p35, and exposed to amyloid-β protein (Aβ(1-42)). These conditions resulted in impaired maturation and neurite outgrowth in vitro, and these effects were reversed by pharmacological or genetic inhibition of CDK5. Similarly, neurogenesis was impaired in a transgenic mouse model of AD that expresses high levels of amyloid precursor protein (APP), and this effect was reversed in transgenic mice crossed with a CDK5 heterozygous-deficient mouse line. A similar rescue effect was observed in APP transgenic mice treated with Roscovitine, a pharmacological inhibitor of CDK5. Taken together, these data suggest that the CDK5 signaling pathway has a critical role in maintaining the integrity of NPCs and neuronal maturation in the adult hippocampus. Moreover, potential therapeutic approaches could focus on modulating the aberrant activity of CDK5 to target the neurogenic and neurodegenerative alterations in AD.

fig2: Morphological and maturation alterations in NPC-derived neural progeny expressing p35 and treated with Aβ. Differentiating NPCs were infected with an adenoviral vector expressing p35 or vector control on day 2 of differentiation, and then treated with 1 μM Aβ or vehicle control on day 3 for 24 h, followed by fixation with paraformaldehyde. Samples were processed for double-immunolabeling with antibodies against p35 and markers of proliferative and neuronal differentiation status (neuronal, β-III tubulin (Tuj1), and doublecortin (DCX); progenitor cells, nestin). (a–f) Double-labeling analysis with Tuj1 and p35 antibodies in vector-infected NPC-derived neural progeny treated with vehicle control (a–c) or Aβ (d–f) for 24 h. (g–l) Double-labeling analysis with Tuj1 and p35 antibodies in p35-expressing NPC-derived neural progeny treated with vehicle control (g–i) or Aβ (j–l) for 24 h. (j–r) In combined p35/Aβ-treated cultures, progeny acquired an abnormal stellate morphology and cells were co-immunoreactive for markers of proliferation stages (nestin) and neuronal (Tuj1 and DCX) lineage (arrows). (s) Quantitative analysis of proportion of NPC-derived neural progeny co-labeled with Tuj1 and nestin antibodies. Scale bar=15 μm. *P<0.05 compared with vehicle-treated controls by one-way ANOVA with post hoc Dunnett's test (N=3)

Mentions:
Under baseline conditions, by the end of the 4-day differentiation period, the majority (>90%) of NPC-derived progeny were immunopositive for β-III-tubulin (Tuj1) (Figures 2a–c, Supplementary Figure 1H), suggesting that these cells represent predominantly immature neurons. In order to determine whether activation of CDK5 was associated with any measurable differences in neuronal maturation, neurite outgrowth was assessed in p35/Aβ-treated NPC-derived neural progeny (Figures 1j–n). β-Tubulin immunofluorescence and neurite outgrowth studies revealed that p35 and Aβ treatment alone or in combination resulted in shorter processes in NPC-derived neural progeny compared with vehicle-treated controls (Figures 1j–n); however, other controls for Aβ (reverse Aβ42−1 peptide) and aggregating proteins (transthyretin (TTR)) had no significant effects on neurite outgrowth (not shown).

Bottom Line:
Neurodegeneration in AD has been associated with aberrant signaling through the cyclin-dependent kinase-5 (CDK5) pathway via its activators p35/p25; however, the role of CDK5 in the mechanisms of defective adult neurogenesis in AD is unknown.These conditions resulted in impaired maturation and neurite outgrowth in vitro, and these effects were reversed by pharmacological or genetic inhibition of CDK5.Moreover, potential therapeutic approaches could focus on modulating the aberrant activity of CDK5 to target the neurogenic and neurodegenerative alterations in AD.

ABSTRACTRecent studies show that in Alzheimer's disease (AD), alterations in neurogenesis contribute to the neurodegenerative process. Neurodegeneration in AD has been associated with aberrant signaling through the cyclin-dependent kinase-5 (CDK5) pathway via its activators p35/p25; however, the role of CDK5 in the mechanisms of defective adult neurogenesis in AD is unknown. First, to study AD-like abnormal activation of CDK5 signaling in an in vitro model of neurogenesis, neuronal progenitor cells (NPCs) were infected with a viral vector expressing p35, and exposed to amyloid-β protein (Aβ(1-42)). These conditions resulted in impaired maturation and neurite outgrowth in vitro, and these effects were reversed by pharmacological or genetic inhibition of CDK5. Similarly, neurogenesis was impaired in a transgenic mouse model of AD that expresses high levels of amyloid precursor protein (APP), and this effect was reversed in transgenic mice crossed with a CDK5 heterozygous-deficient mouse line. A similar rescue effect was observed in APP transgenic mice treated with Roscovitine, a pharmacological inhibitor of CDK5. Taken together, these data suggest that the CDK5 signaling pathway has a critical role in maintaining the integrity of NPCs and neuronal maturation in the adult hippocampus. Moreover, potential therapeutic approaches could focus on modulating the aberrant activity of CDK5 to target the neurogenic and neurodegenerative alterations in AD.